1. Field of the Invention
The present invention relates to a toothed belt and, more particularly, to a toothed belt having a plurality of elastic teeth. The toothed belt wraps around a plurality of toothed pulleys so that the elastic teeth of the toothed belt engage the teeth of the toothed pulleys so as to transfer motion. Reduced localized concentration of stress and increased durability are thereby provided. The present invention further relates to a toothed belt-adapted pulley having a plurality of teeth with the toothed belt wrapped therearound. More particularly, it relates to a toothed belt-adapted pulley having increased durability, which provides reduced localized concentration of stress on the toothed belt.
2. Description of the Related Art
Conventionally, in a commonly used toothed belt, trapezoidal elastic teeth were equal or smaller in height than the tooth spaces of a pulley. In a toothed belt-adapted pulley for use in combination with the toothed belt, the depth of each tooth space of the pulley was equal to or greater than the tooth height of the toothed belt. In such a combination of the toothed belt and the toothed belt-adapted pulley, the toothed belt has problems in which: (1) stress concentration occurs at dedendum portions when tooth portions are subjected to shearing stresses; (2) interference is likely to occur when the tooth tip portions and the pulley are brought into and out of engagement with one another; and, (3) during engagement, a localized bend will occur in tensile cords which is affixed to the belt. As a result, belt life is decreased, and transferable loads are limited to within a small range.
In order to overcome the above problems, various toothed belts having improved tooth profiles have been proposed, and further, have been commercialized. For example, Japanese Examined Patent Publication Nos. 56-29141, and 57-51589 describe a toothed belt, in which elastic teeth have a height greater than the depth of the tooth spaces of the pulleys so that tip portions of the elastic teeth are pressed against bottom portions of the pulley tooth spaces during engagement. This pressing effect reduces localized deformation (or maximal curvature) of tensile cords that remains affixed to bottom portions of the elastic teeth. The toothed belt enables the smooth arcuate formation of tensile cords portion during engagement with the pulleys. This prevents localized bending of the tensile cords when the toothed belt is engaged with the pulleys. Belt life is also increased. Further, Japanese Examined Patent Publication Nos. 52-20629, 57-1714, and 56-37457 teach a technique for providing a belt having a high-load capacity, low noise, and long life, in which elastic teeth are formed into an arcuate pattern so as to prevent the occurrence of stress concentration and strain on dedendum portions in a manner similar to the trapezoidal teeth. (In addition, according to embodiments and related commercial goods, the elastic teeth have a height greater than the depth of the tooth spaces of the pulleys to be engaged therewith. This configuration aids in pressing the tooth tip portions against the bottom portions of the pulley tooth spaces in a manner similar to the aforesaid related art.)
The above-described techniques have improved the shortcomings of trapezoidal teeth. In the former reference, however, a strong bending still remains although the localized bending of the belt tensile cords is partially attenuated. In addition, concentration of stress on the dedendum portions cannot be successfully prevented. In latter reference, the elastic teeth have an arcuate pattern, but the dedendum portions are the same as the conventional dedendum portions. As a result, stress concentration on the dedendum portions is attenuated to some extent during engagement off the belt with the pulleys; however, the resulting effectiveness is still insufficient. In either case, the use of the elastic teeth for long periods of time results in cracks in the dedendum portions, and belt durability has been insufficient.
An object of the present invention is to provide a toothed belt having usability under high loads, with high durability, and reduced noise, and in which localized bending of the belt tensile cords as well as stress concentration and strain on dedendum portions are prevented through improvements in the form of the elastic teeth of the toothed belt and similar improvements in the pulleys which accommodate the elastic teeth. A further object of the present invention is to provide a toothed belt having the aforesaid high durability and reduced noise, in which no skipping occurs, even under high loads.
Another object of the present invention is to provide a newly shaped, toothed belt-adapted pulley, which is used with the aforesaid improved toothed belt to be engaged therewith. The pulley minimizes interference when being driven into and out of engagement with the toothed belt, thereby allowing smooth engagement therewith. A still further object of the present invention is to provide a combination of the newly shaped, toothed belt-adapted pulley and the toothed belt having high durability, in which reduced vibration and low noise are achieved, and smooth engagement is provided without skipping under high loads.